aerial photograph of Cow Castle Iron Age hill fort in the Exmoor National Park, Somerset, England UK. Cow Castle is a slight univallate hillfort ( small, single ditch and bank ) dating from some time in the Late Bronze Age to the Early Iron Age , ie between the eighth and fifth centuries BC. Slight univallate hillforts are relatively rare with there being about 150 in the UK. Cow Castle is a significant example with it's well chosen defensive position on a Knoll above the River Barl valley and it's good state of preservation.